In recent years, plastic materials have been used in a wide range of applications because of their characteristics such as easy molding processing and lightness. Particularly important performances required in an optical member such as an optical lens include a high Abbe's number, a low specific gravity, moldability, heat resistance, light resistance, high hardness, low water absorbability, and distortion accuracy of a molded article.
Conventionally, such kind of lens has been molded by a method such as a press method or a cast method. The former, i.e., the press method is low in productivity because production is performed by a cycle of heating, pressurizing, and cooling. Meanwhile, the latter, i.e., the cast method has problems in that polymerization is performed by pouring a monomer in a mold, which elongates a production time, and many molds are required, which increases a production cost. In order to solve such problems, various proposals on use of a UV light curable resin composition have been made (Patent Literatures 1 and 2).
A method of producing a transmission type screen by using such UV light curable resin composition has been successful to some extent. However, such conventional resin composition has problems such as poor adhesion to a substrate and poor mold release property from a mold. When the resin composition has poor adhesion, the kind of the substrate which may be used is limited, resulting in a difficulty in obtaining intended optical properties. When the resin composition has poor mold release property, it becomes impossible to use the mold because the resin remains in the mold when being released from the mold. In addition, there are also problems in that a resin composition having good adhesion can adhere to a mold sufficiently, and hence is liable to have poor mold release property, while a resin composition having good mold release property is liable to have poor adhesion. Therefore, it has been desired to provide a resin composition which satisfies both performances of the adhesion to a substrate and mold release property from a mold.
For example, Patent Literature 3 proposes an active energy ray curable resin composition having an oxetane ring, describing that the resin composition is excellent in mold release property, but does not disclose the adhesion to a substrate.
Patent Literature 4 proposes a UV light curable resin composition obtained by blending a (meth)acrylate-based monomer in a polymer having specified refractive index and molecular weight. The literature describes that the resin composition including a methyl methacrylate-based (co)polymer as a major component is excellent in adhesion to a substrate, but does not disclose its mold release property.
Patent Literature 5 discloses that a molded plastic lens has good heat resistance. However, the heat resistance disclosed in the literature was evaluated by allowing the lens to stand in a constant temperature room at a temperature of 70° and a humidity of 60% for 24 hours and then observing its outer appearance such as its shape and whitening. Therefore, with regard to the heat resistance under an extremely severe environment of more than 260° C. in solder reflow required for an optical member used in an advanced technology field, a molded lens produced in accordance with a technology disclosed in the literature is not suitable in actual use because the lens undergoes a change in color and a reduction in spectral transmittance under a severe temperature condition owing to the fact that the lens contains a urethane bond.
Patent Literature 6 discloses a photosensitive resin composition for optical use including a polymer substance containing a structural unit including a carbon-carbon double bond in its molecular side chain and a (meth)acrylate. However, the polymer substance containing a structural unit including a carbon-carbon double bond in its molecular side chain, disclosed in this patent literature, has insufficient water absorbability as an optical member used in an advanced technology field and has industrially insufficient mold release property. Further, the patent literature does not suggest that introduction of an end group having a specific structure into the polymer substance can significantly improve properties such as low absorbability and mold release property, and it has been impossible to imagine the fact.
Further, Patent Literature 7 discloses a photosensitive resin composition for a hard-coating agent, which contains a compound (A) having at least two ethylenically unsaturated groups in a molecule, a polymer compound (B), and a photopolymerization initiator (C). However, the polymer compound (B) has no polymerizable group and has problems in reactivity, strength, and heat resistance.